Sane judgment abhors nothing so much as a picture perpetrated with no technical knowledge, although with plenty of care and diligence. Now the sole reason why painters of this sort are not aware of their own error is that they have not learnt Geometry, without which no one can either be or become an absolute artist; but the blame for this should be laid upon their masters, who are themselves ignorant of this art.

The Art of Measurement (1525).

Whoever … proves his point and demonstrates the prime truth geometrically should be believed by all the world, for there we are captured.

Vier Bücher von menschlicher Proportion (1528).

But I shall let the little I have learnt go forth into the day in order that someone better than I may guess the truth, and in his work may prove and rebuke my error. At this I shall rejoice that I was yet a means whereby this truth has come to light.

The opening quotation of Introduction, Conjectures and refutations: The Growth of Scientific Knowledge by Karl Popper (1963).

The new art must be based upon science — in particular, upon mathematics, as the most exact, logical, and graphically constructive of the sciences.

My father suffered much and toiled painfully all his life, for he had no resources other than the proceeds of his trade from which to support himself and his wife and family. He led an honest, God-fearing life. His character was gentle and patient. He was friendly towards all and full of gratitude to his Maker. He cared little for society and nothing for worldly amusements. A man of very few words and deeply pious, he paid great attention to the religious education of his children. His most earnest hope was that the high principles he instilled into their minds would render them ever more worthy of divine protection and the sympathy of mankind. He told us every day that we must love God and be honourable in our dealings with our neighbours.

Of Dürer's father, also named Albrecht, as quoted in Albrecht Dürer : his life and work (1960) by M Brion.